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Battery Management - Chargers Forum
bq24747 "Input Overvoltage Protection" feature: Typo?
The features page of the bq24747 datasheet mentions that it features "Input Overvoltage Protection (OVP)" - however, the datasheet then *does not* go on to mention this feature at all. Does the bq24747 actually have this feature? If so, what voltage is an "overvoltage"?
I would like to protect the chip from reverse polarity and overvoltage conditions (i.e. in case an incorrect adapter is connected) - but it also seems that all of TI's Charger Front-end Protection chips are for 1-cell and 2-cell applications only (my charger is 15V for 3 cells).
Any suggestions would be greatly appreciated.
When DCIN is greater than 4 V and ACIN is greater than 2.4 V, the adapter is considered to be present. In this condition, both the VDDP and VREF function properly and battery charging is allowed. Otherwise, the charging is not allowed.
The same as the battery-current regulation, adaptor current is sensed by resistor RAC connected between the CSSP and CSSN pins. The maximum full-scale differential voltage between CSSP and CSSN is 110.08 mV. Thus, for a 0.010Ω sense resistor, the maximum input current is 11.008 A. For any system current greater than the max adapter current, the Dynamic Power Management will start. By using DPM, the input current regulator reduces the charging current when the input current exceeds the limit set by the Input Current.
Thanks for the reply Tahar!
However, my question was regarding the Input Overvoltage Protection (OVP) feature mentioned on the first page of the bq24747 datasheet (not the adapter detect/undervoltage feature).
Do you have info regarding the OVP feature?
bq24747 doesn't have input OVP function. bq24745 has a more accuarcy datasheet. Please use it as reference.
bq24725 has a input OVP function.
I see - so it is indeed a typo in the bq24747 datasheet then?
Can the bq24725 provide a "wake-up" signal to deeply discharged batteries in a non-host config. (like the bq24747 Vddp)?
After looking at the bq24725 datasheet, it looks like the bq24725 REGN output is practically the same as the bq24747's VDDP output... So I guess the bq24725 may be suitable for a non-host config? Could you please verify this Wang.
Thanks in advance :)
No. bq24725 doesn't have 3.3V VREF. So, REGN is also an internal reference. So, it is not good to be a "wake-up" source.
Would you be able to elaborate a bit more on this point? Why does being an internal reference make REGN unsuitable?
bq24725 needs a external LDO to provide a "wake-up" signal to deeply discharged battery. We are working on that application note.
A deeply discharged battery voltage could be zero voltage. If the bq24725's REGN is zero, there is no interal reference, the ACDRV or HIDRV logic circuit may not work.
I see - thanks!
I look forward to reading the application note on this configuration :)
I am currently working on this application note, I will send a draft to you as soon as I get most of it done and have some results in the lab verified.
That's great news!
Please let me know when the draft is available.
Any update on the draft of that app note?
I'm attempting to get the bq24725EVM working with the bq20z65-R1EVM at the moment (in a non-host config).
The bq24725 seems to be receiving the broadcast voltage and current commands from the gas-gauge (confirmed by checking the bq24725 software) - but the charging just won't actually start! Very strange...
Only after I "kick-start" it with a charging current (sent from the bq24725 software) lower (e.g. 500mA) than the broadcast current (1.5A) that charging starts...
EDIT: The charger then jumps back up to the broadcast current after this "kickstart" from the software... Strange.
EDIT 2: Setup seems to work fine when I connect the DC adapter power supply (19V) and then the logic supply 3.3V supply by turning it on by increasing/ramping the voltage 0V to 3.3V.
EDIT 3: Found the cause of the charging problem. When charging is due to start, ACOK starts fluctuating rapidly (between 0V and maybe 2.5V) thus preventing charging from starting. What could be the cause of this? This also occurs when a system load is connected while charging is in progress.
We tested bq20z90+bq24726. It works. So, the bq24725+bq20z65 should work. Is the 3.3V pull-up source available all the time during your test?
Please monitor ACDET voltage and Vcc voltage. Do the ACDET and VCC have a glitch?
Charger is receiving the broadcasts from the gas gauge it seems.
V(ACDET)=2.65V +/- 1mV (when Vsupply=19.9V)
VCC=19.64V +/- 1mV
So both are pretty stable and are not fluctuating significantly (at least not below the UVLO or Adapter Detection thresholds)
ACOK is oscillating still though... The pull-up source for this signal is REGN (see the bq24725EVM schematic) - I also tried pulling ACOK up to the 3.3V supply using a ~10k resistor - no difference to the oscillations! As a consequence, ACDRV is also oscillating causing Q1 to switch on and off continuously - this is why charging is not starting.
Also, REGN (the pull-up on ACOK) is STABLE at 6.068V!
Furthermore, the external 3.3V power supply only pulls up the SMBus data lines and ILIM signal (as per the schematic) - i.e. not ACOK.
EDIT: ACOK stabilizes at 3.3V after turning OFF the 3.3V external supply by decreasing to 0V - when the supply is increased back to 3.3V, ACOK remains stable and charging begins - strange indeed!
EDIT 2: The oscillations of ACOK only occur when a battery pack is connected across GND and BAT. The oscillations STOP when the battery is disconnected momentarily (from either BAT or GND) and then reconnected - charging then begins. Oscillation rate decreases when Deglitch Time is set to 1.3s. I hope I've now given enough information for this fault to hopefully be replicated in the lab.
EDIT 3: SOLVED! Turns out my bench power supply was experiencing fast voltage dips which were going below the ACOK threshold. A 470uF cap on the supply has fixed all the issues. Overlooked the possibility of this being the cause of the issue as I originally thought the supply would be more than capable of supplying the peak-current during charging - turns out it wasn't.
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